IMPROVED MULTILAYER POROUS MEMBRANES AND METHODS OF MAKING THE SAME

A multilayer membrane comprising at least two co-extruded layers where the two co-extruded layer contain different polymers and one of the two co-extruded layers contains an extrusion additive. Examples of useful extrusion additives may include a nucleating agent or a pore-forming particulate. A method for making the membrane is also disclosed. Using an extrusion additive when co-extruding two different polymers avoids some of the drawbacks associated with processes involving the co-extrusion of different polymers, particularly processes where a co-extruded non-porous precursor is later stretched to form pores. For example, the drawback of lower permeability, difficulty to make lower Gurley, and splittiness may be improved.